The term gas shall be used herein so as to also include vapour while the term liquid also includes liquid containing gas such as froth. The expression treating liquid is used to indicate compounds, preferably liquids, which selectively removes contaminants such as hydrogen sulphide and/or carbon dioxide by physical and/or chemical phenomena.
Trays for gas/liquid mass transfer containing a cyclonic gas/liquid separation device differ from regular mass transfer trays in their range of applications. A tray in which gas and liquid are contacted and subsequently separated with a cyclonic gas/liquid device can be made significantly more compact than a regular tray where the separation between gas and liquid is by gravitational forces instead of centrifugal forces.
U.S. Pat. No. 6,227,524 describes contact and separation elements (CSE's) for high speed mass transfer trays in which liquid enters the CSE through an annular row of holes into a grid net of vertical vanes dispersing the liquid into small droplets which together with the gas move to the vanes of an axial swirler located directly above the vertical vanes in which swirler the liquid-gas flow is subjected to a rotary motion thereby creating an upwardly moving rotating liquid film. The final gas/liquid separation takes place in the separation zone located in the upper part of the CSE, while the mass transfer mainly takes place in a small zone just above the liquid inlet holes. The amount of liquid entering the contact zone depends on a force balance where the liquid level (as set by the height of the weir) around the CSE provides a hydrostatic force for liquid to enter the CSE. In addition the gas flow inside the CSE induces a suction force which increases inflow of liquid into the CSE. These two forces are balanced by a counterforce resulting from a pressure drop over the CSE, particularly induced by the swirler and the narrowing transition between the upstream contact zone and the downstream separation zone. Ultimately the maximum capacity of this CSE will depend on the pressure balance: as the gas rate to the device is increased the pressure drop will increase. When the pressure drop inside the contact zone exceeds a certain value (which depends on the liquid height surrounding the CSE) part of the gas will escape through the liquid inlets at which point the mass-transfer performance will drop dramatically.
EP-A-0048508 describes an apparatus for treating mixtures of liquid and gas at high flow velocities and/or high liquid loads. The liquid flows through in once-through mode, i.e. without internal recycle. Furthermore, the volume of the contact zone is small compared to the volume of the separation zone and the swirler is located in the bottom part of contact and separation unit.
The mass transfer rate is related to the amount of liquid entrained per unit of gas in the contact zone. The required volumetric mass transfer rates increase with higher partial pressure of the impurities (such as CO2) to be absorbed. However, mass transfer rates obtainable with prior art contact and separation columns were found to be limited.
In offshore gas mining contact and separation columns are used with floating applications, e.g. on a floating device or boat. Sea motion induced sloshing or waving of the liquid poses serious limitations on the obtainable mass transfer and the effectiveness of the columns.
It is an object of the invention to provide contact and separation equipment enabling improved mass transfer.
It is a further object of the invention to provide robust contact and separation equipment which can be used with floating applications.